Related products under the same brand form a product line. A company that sells several models of smartphones, or a range of skin-care items that share a common formulation philosophy, is offering a product line. The line may vary in features, price, or target segment while maintaining a coherent identity.

Managing a product line involves decisions about width (how many different lines), length (how many items in a line), and depth (how many variants of each item). Adding items can capture more customers; pruning items can reduce complexity and cost. Cannibalization—when a new item steals sales from existing ones—must be weighed against overall line growth.

A strong product line gives customers clear choices within a trusted brand and gives the company efficiencies in development, production, and marketing. Weak or overlapping items dilute focus. Regular review of the line’s performance and of customer needs keeps the assortment relevant.